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Preamp for Quad 405?

Discussion in 'classic' started by murphydog, Feb 12, 2019 at 11:42 AM.

  1. murphydog

    murphydog Canine member

    I’ve recently bought an upgraded 405 for my second system from a fellow fisher. I’m very happy with it.
    However I’ve found that my zero gain Croft Basic struggles to drive Harbeth P3 s to a reasonable volume.
    I’m also using a NVA passive which is better but precludes vinyl replay. Suggestions would be welcome for a low-ish budget solution. One option I have identified is a 34 pre. Opinions seem to very somewhat about the Quad pres however.
     
  2. Tony L

    Tony L Administrator

    Altering the gain of the Croft pre is as simple as swapping two resistors. If you contact Glen he’ll tell you which ones!
     
  3. murphydog

    murphydog Canine member

    That’s good advice, I’ve contacted him.
     
  4. eastone

    eastone pfm Member

    Is it possible the input sensitivity of the 405 was altered when it was upgraded? In stock form it should be able to drive P3s easily with a passive pre.
     
  5. Tony L

    Tony L Administrator

    Agreed. The standard spec is 0.5V isn’t it? (same as a 303).
     
  6. murphydog

    murphydog Canine member

    Glenn tells me that it the Croft needs to go back to him to have the gain increased. Would it be a simple matter to check the Quad sensitivity?
     
  7. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Only if you have the required test gear.... so probably no...
     
  8. Zombie

    Zombie pfm Member

    Send the 405 to Glenn too. He prob has the gear.
     
  9. Tony L

    Tony L Administrator

    I’d start by googling Quad 405 input gain or sensitivity reduction. Chances are it just involves changing a resistor or two per channel. I know Rob knows how to do it. Once understood identifying what is in there currently shouldn’t be too hard, i.e. just reading a couple of colour codes. That will tell you in the amp has been modified or not. Thinking about it my suspicion is it will have been. I could very happily drive inefficient JR149s with a 303 and a passive preamp with the knob somewhere around the mid-point on CD, and the 405 is the same sensitivity but 3db or so more powerful. I’d expect the ‘zero-gain’ Croft to behave like a passive from a volume perspective.
     
  10. eastone

    eastone pfm Member

    I think so. 1.5V is pretty common on upgraded units. Reducing the Quad's input sensitivity does benefit noise reduction so I think if it was me I'd be inclined to add some gain in the Croft. Then again you may have a particular preference for passive preamps, in which case the Quad can be easily reverted.
     
  11. murphydog

    murphydog Canine member

    That chimes with my reading around various upgrade threads. I like the Croft especially the phono stage so I think I’ll
    get it off to Glenn.
     
    eastone likes this.

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